The _needs_trusted_identity_retry method was hard-coding specific
server-side error strings to detect when a request failed due to
missing X-OpenViking-Account / X-OpenViking-User headers. Each new
server-side error variant required another string added to the client.
Replace the string enumeration with a structural match: the error
message mentions one of the tenant headers AND the HTTP status is 400.
This covers all current error variants:
- "Trusted mode requests must include X-OpenViking-Account and User"
- "ROOT requests to tenant-scoped APIs must include X-OpenViking-Account"
- "Trusted mode requests must include X-OpenViking-Account."
- "Trusted mode requests must include X-OpenViking-User."
The 400 status guard avoids false-positives on 403 errors such as
"USER API keys cannot override X-OpenViking-User", which must not
trigger a retry.
All 176 existing tests pass.
(cherry picked from commit 5a24d6766ce1ae89b20266b751c5746a8243c378)